By the fault analysis of digital transmission paths, the influence of faults on the transmission paths is detected. Faults in the transmission of binary data have the effect that a transmitted logic "1" is received as "0" and vice versa. Such transmission errors are recognized through fault analysis in pulse code-modulated (PCM) systems by comparison of a received serial data stream with a transmitted data stream as reference data stream. Generally the transmitted data stream consists of apparently random binary sequences (quasi-random sequences), which are generated for example by means of a regenerative shift register at the site of transmission and reception. Now if in the comparison of the received data stream with the reference data stream bits transmitted error-free are marked by a "0" and bits transmitted wrong by a "1", one obtains at the output of the transmission path the "bit error pattern." In the evaluation of such bit error patterns it is then possible, for one thing, by simply viewing them, to recognize sensitive points of the transmission line relative to certain transmission patterns, and for another, by further processing of the bit error pattern in mathematical algorithms, statements can be made about stochastic and systematic transmission errors for determining the causes thereof.